In well production apparatus and particularly that used in offshore wells, a subsurface safety valve may be installed in the tubing string to provide a means by way of which fluid flow to the head of the well may be cut-off beneath the sea floor should it become necessary to do so. Typically, such safety valves are maintained open for fluid flow to the well head through the use of a control pressure communicated to a safety valve through a control line extending from the well head to the valve. A surface hanger supports an upper section of the tubing string extending downwardly through the well casing from the well head and connecting to the safety valve. Beneath the safety valve, a lower section of the tubing string is suspended in the casing by a subsurface tubing hanger. When set in the casing, hydraulically actuated slips protrude radially from the hanger to embed in the interior wall of the casing to support the lower section of the tubing string upwardly within the casing. U.S. Pat. No. 3,874,446 discloses one form of a tubing hanger having hydraulically actuated slips.
Additional support for the tubing string may be provided between the casing and the tubing string by vertically spaced sets of packers such as may be installed in the casing in a permanent or semi-permanent fashion. It is important when installing the tubing string in the well that the upper section of the tubing string be supported entirely by the surface hanger and associated sealing members to insure proper sealing between the tubing string and inside of the casing. Also, it is important that the lower section of the tubing string be supported by the subsurface hanger without weight from the lower section of the tubing string being carried by the surface hanger. Before the subsurface hanger is set within the casing, the weight of the lower section of the tubing stretches the upper section of tubing a finite amount, dependent in part upon the elasticity of the material from which the upper section of tubing is formed. Accordingly, when setting the subsurface hanger, the latter is positioned in the casing upwardly of its position with the tubing stretched and is set to carry the weight of the lower section of tubing. Thereafter, the upper section of tubing is lowered to seat the sealing members with the tubing contracting some extent. To allow for this without imposing a lifting force upon either the subsurface hanger or the surface hanger, an expandable joint is provided in the upper section of the tubing.
One type of well production apparatus of the foregoing general character is disclosed in U.S. Pat. No. 4,051,894. In this prior art apparatus, an expandable joint in the form of a rotational spacer is attached to the lower end of a safety valve and a seal assembly including a seal assembly body or stinger is telescoped with a receptacle connected to the upper end of a subsurface tubing hanger. Adjustment of the length of the spacer is achieved by relative rotation of the safety valve and spacer.